The prior art discloses various types of disk files that are employed to store data in information handling systems. A disk file comprises generally one or more disks each having a magnetic surface for storing data. The disks are mounted on a spindle and continually rotated at a constant speed. A magnetic transducer is mounted on a head arm assembly which cooperates with the magnetic surface of the disk and is movable by an actuator to preselected concentric recording tracks under the control of an address signal supplied to the actuator from the data processing system. The transducer is lightly biased toward the disk surface and is spaced therefrom by a film of air as the disk is rotated. This type head is sometimes referred to in the art as an air bearing type head. The transducer is supplied with data signals during the data storage operation. During reading of stored data the transducer senses the magnetic transitions which are converted to data for use by the system.
Disk file configurations vary in the number of disks employed, the size of the disks, and the type of actuators that are employed to position the magnetic head to an addressed recording track. Since total storage capacity of a disk file has, in recent years, become an important parameter, most file configurations employ a plurality of disks mounted on a common spindle, with each disc surface having a separate magnetic transducer associated with it.
Two general types of electromagnetic actuators have been used for positioning the magnetic heads. In one type of actuator, the heads are moved during the track accessing operation in a straight line which generally follows a radial line through the center of the spindle. The second type of actuator is referred to as a rotary actuator. This type actuator moves the head during the track accessing operation on an arc substantially normal to the tracks. In both actuator types, the individually manufactured head-arm assemblies that are associated with each disk surface must be assembled into a comb type structure with the transducers at the distal ends of the head arms accurately aligned vertically.
The personal computer and in particular the so called "lap top" models of personal computers, have imposed a size parameter on disk files which is in total opposition to the currently desired capacity requirements for data storage. Stated differently, as the need for more storage capacity is increasing, the size requirements for disk storage drives is decreasing.
Disk diameter is the dominating factor in determining the foot print of the drive. The number of disks in the stack generally determines the height of the drive. In the last few years disk diameters for fixed disk drives used in personal computers have decreased from five and one-quarter inches to three and one-half, to one and one-eighth inches. Prototype disk files employing one inch disks are discussed currently in the literature. The decrease in size has had little or no impact on storage capacity, in that the various technologies which directly affect capacity, such as linear recording density and track density, have been substantially improved.
In recent years substantial increases in track density have been made as a result of improvements in magnetic head technology, the recording channel circuits, and the magnetic head positioning systems. Substantially all state of the art disk drives have head positioning systems which employ a servo control system supplied with servo signals developed from reading prerecorded servo data from the disk, to maintain the transducer precisely over the center of the addressed track.
A technique called "sector-servoing" is currently employed in many drives to develop the servo control signals. The concept of sector servoing involves formatting each of the concentric tracks on the disk in alternate sectors of servo data and regular data. The sections of tracks in the sectors containing servo data have a pre-recorded servo pattern which can produce a correction signal that is supplied to the servo system to continuously reposition the head to the center of the track only as the head is scanning the servo sector. No corrective action on the position of the head relative to a track can be achieved when the head is scanning a data sector and data is being transferred to or from the system.
It will be seen that the sector servoing technique always requires a compromise to achieve the optimum percentage of track used for servo data. The designer can improve the positioning accuracy of the positioning system, and hence increase track density by using more of the recording track for servo data. However, using more of the track for servo data reduces the data capacity of the track.
Another technique that has been suggested in the art is referred to as a "buried servo" technique. This technique requires a special two layer disk in which the bottom layer is a high coercively pre-recorded servo layer and the upper layer is a lower coercivity data recording layer. The servo data is recorded under high field conditions so that normal data recording at lower field levels does not affect the previously recorded servo data. In use the servo data is filtered out of the read channel signal and supplied to the positioning system.
While the buried servo technique can supply servo signals concurrently with recording and reading of data, it has not been readily accepted in that the cost of applying the two layers of magnetic material having different coercivities has proved to be uneconomical.
Another arrangement that has been used in disk files having a relatively large number of stacked disks involves the concept of dedicating one disk surface for servo tracks and the remaining disk surfaces to data. If the disk stack has for example 50 disk surfaces and only one is used for servo data, the percentage of disk space devoted to the servo function is only slightly more than two percent. However, as the number of disks in a stack decreases, the percentage increases. Since, track densities and linear recording densities have increased so dramatically in recent years, the need for disk stacks heaving a large number of disks has evaporated.
The present invention provides a method and system in which servo signals are developed from a single layer magnetic surface on which data tracks are defined by a servo pattern that has been pre-recorded on the same single magnetic layer used for storing data and can be recovered by the same transducer.